The treatment of acute and chronic spinal instabilities or deformities of the thoracic, lumbar, and sacral spine has traditionally involved the implantation of rigid rods to secure the vertebrae of a patient. More recently, flexible materials have been utilized in connection with anchor members, e.g., pedicle screws, to provide a dynamic stabilization of the spinal column. Such dynamic stabilization systems or implants typically include a flexible member positioned between pedicle screws installed in adjacent vertebrae of a person's spine.
Certain dynamic stabilization systems permit the top loading of a flexible member and connecting member between pedicle screws. One such top loading system is disclosed in U.S. Patent Application Publication No. 2002/0035366 to Walder et al., titled “Pedicle Screw For Intervertebral Support Elements”, which is expressly incorporated by reference herein in its entirety. Another top loading system is disclosed in U.S. patent application Ser. No. 11/618,943 to Hestad et al., titled “Spine Stiffening Device”, which is expressly incorporated by reference herein in its entirety. Still other dynamic stabilization systems are adapted to securely retain the flexible member between pedicle screws without the use of a connecting member.
While current dynamic stabilization systems include flexible members, these flexible members are known to be composed, for example, of a specific material having a singular elasticity that does not allow for variability in flexibility, except by varying the length of the flexible member between pedicle screws. In other words, those flexible members provide an equal bending force in all directions, i.e., the flexible member is without variable flexibility. Such variability in flexibility could provide surgeons with greater options in selecting the most appropriate flexible member for placement at a specific location along a patient's spine, such selection being dictated by the desired bending movement of the flexible member at that location.
Accordingly, it would be desirable to provide flexible members having variable flexibility for use with dynamic stabilization systems to provide dynamic stability to a person's spine that addresses these and other deficiencies of current flexible members.